Rheological properties of creams with four different surfactant combinations - effect of storage time and conditions

Changes in the theological properties of four o/w cream formulations differ ing in the combination of surfactants were studied. The non-ionic surfactan ts used were soybean derivatives, polyethylene glycol 10 and 25 soya sterol , and sorbitol derivatives, sorbitan monooleate and trioleate. Combinations of the soybean and sorbitol derivatives were used. The theological propert ies were tested during a 28-day storage period at three different storage c onditions (cold, room temperature and accelerated conditions). In addition to dynamic and static theological tests, droplet size distributions and con ductivities of the creams were also determined. The consistency of the crea ms containing polyethylene glycol 10 soya sterol decreased during storage. Despite the greatest decreases in consistency, the creams containing polyet hylene glycol 10 soya sterol exhibited the most viscoelastic structures wit h linear viscoelastic behaviour. Storing the creams for 28 days in the thre e different storage conditions made the differences in the consistency of t he formulations smaller. All three storage conditions were involved when th e conditions of the most viscoelastic cream of each formulation was specifi ed. In the case of linearly viscoelastically behaving creams containing pol yethylene glycol 10 soya sterol, all the theological tests correlated with the droplet size distributions and the conductivity tests. (C) 2001 Elsevie r Science B.V. All rights reserved.